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Biomedical subjects

B Wiggert

Publications and source records attributed to B Wiggert.

At least 163 records · Page 9Linked to original sources
PubMed1983

Changes in retinoid binding levels during development of the chicken cornea.

[3H]-retinol binding to cellular retinol-binding protein (CRBP) increased more than five-fold in developing chicken corneal epithelium at 14 days of incubation, the time when the initial increase in corneal transparency occurs in the developing embryo. In contrast, [3H]-retinoic acid binding to cellular retinoic acid-binding protein (CRABP) was highest at the earliest stages and decreased progressively to a very low level in the corneal epithelium near the time of hatching. Thus, there appear to be changing and differing requirements for retinol and retinoic acid during development of the chicken cornea.

Animals↗
PubMed1982

Interphotoreceptor retinol-binding proteins: possible transport vehicles between compartments of the retina.

In the eye, vitamin A (retinol) is mainly stored in the retinal pigment epithelium(RPE) although its primary function is in the visual process in the photoreceptor organelles of the neural retina (NR). It is well established that during light adaptation, the amount of retinol drops in the NR but rises in the RPE. During dark adaptation, the converse occurs. This indicates a migration of retinoid between the two tissues, the direction of which is dictated by the state of light or dark adaptation of the photoreceptors. The mechanism by which this migration is effected is unknown. We now present evidence that at least one protein exists in the subretinal space or on the cell surfaces which demonstrates many of the unique characteristics one would expect of an interphotoreceptor retinol-binding protein and could function as a vitamin A transport vehicle between NR and RPE.

Adaptation, Ocular↗
PubMed1980

Retinal pigment epithelial cell differentiation in vitro. Influence of culture medium.

Cultured chick pigment epithelial (PE) cells from stages 29 to 31 chick embryos grown in normal Eagle's minimum essential medium (MEM) exhibit marked colonial organization and differentiation. Individual cells appear epithelial and heavily pigmented. In contrast, cells grown in Ham's modified F-12 medium appear fibrocytic with colonial disorganization and little visible pigmentation. Biochemically, cells grown in F-12 medium lack receptors for both 3H-retinol and 3H-retinoic acid, although cells grown in MEM exhibit specific 3H-retinol binding. Pathways of glucose utilization differ significantly in cells grown in the two media, with considerably lower overall respiratory activity and lower pentose phosphate pathway activity seen with the F-12 medium. Thus different nutritional states can markedly affect PE cell characteristics in culture and possibly in vivo as well.

Animals↗
PubMed1978

Separation of retinoid receptors from cultured retinoblastoma cells.

Receptor proteins for [3H]retinol and [3H]retinoic acid in cultured human retinoblastoma cells have been separated rapidly and reproducibility by two different methods. By isoelectric focusing, the isoelectric point of the retinol receptor is at pH 4.0; the retinoic acid receptor has a higher isoelectric point of 4.3. Polyacrylamide slab gel electrophoresis revealed a slower migration rate for the [3H]retinoic acid receptor compared to the [3H]retinol receptor. The separate nature of the two proteins has thus been established in this unique human cell line.

Carrier Proteins↗
PubMed1978

Vitamin A receptors. Retinoic acid binding in ocular tissues.

Analysis of the sucrose-density-gradient patterns of the 110 000g supernatant fractions of adult and foetal retina and pigment epithelium showed them to contain a limited number of highly specific binding sites ('receptors') for [3H]retinoic acid that sediment at approx. 2S. Binding in pigment epithelium is higher than in any tissue yet reported. A 5S binding component is also observed and is probably due to serum contamination. Fractionation studies indicate that [3H]retinoic acid binding in the retina is lower in the photoreceptor units than in the retinal inner layers. This is in contrast with previous results that show greater [3H]retinol binding in photoreceptors. Studies with dystrophic human and rat retinas, which lack the photoreceptor layers, confirm that [3H]retinoic acid binding is greater in the non-photoreceptor layers of the retina. No specific [3H]retinoic acid binding is found in corneal epithelium, although endothelium and the conjunctiva demonstrate specific 2S binding. Such differences in retinol and retinoic acid binding may indicate different roles for the two compounds in ocular tissues.

Animals↗
PubMed1977

Vitamin A receptors. I. Comparison of retinol binding to serum retinol-binding protein and to tissue receptors in chick retina and pigment epithelium.

1. A simple, efficient three-step method for purification of serum retinol-binding-protein is described with homogeneity obtained after chromatography on DEAE-Sephadex, CM-Sephadex and Sephadex G-100. 2. Evidence is presented indicating that retinol receptors present in the cytosol fraction of chick retina and pigment epithelium are separate and distinct from purified retinol-binding protein. Fluorescence characteristics are different in tissue cytosol and serum as assessed by sucrose density gradient analysis. Tissue retinol receptors do not interact with human serum prealbumin although the prealbumin readily complexes with purified chicken retinol-binding protein. Likewise, no binding to serum retinol-binding protein antibody could be detected by sucrose density gradient analysis, in immunoprecipitation experiments or by double immunodiffusion. It thus appears that specific retinol receptors are present in neural retina and pigment epithelium that are different from serum retinol-binding protein.

Animals↗
PubMed1977

Vitamin A receptors. II. Characteristics of retinol binding in chick retina and pigment epithelium.

Gel filtration studies demonstrate that retinol receptors of chick retinal and pigment epithelial cytosols are (1) of very similar nature (2) of small molecular size (about 18000 daltons) and are different in character from serum proteins. Citral inhibits the binding of [3H]retinol to the retinal 2 S receptor. Retinol acetate competes with retinol for binding to 2 S receptor in both retina and pigment epithelium whereas retinol palmitate is an effective competitor only in the pigment epithelium. Dithiothreitol maximizes 2 S binding in retina and pigment epithelial cytosol; its absence does not lead to receptor aggregation however. A limited number of high affinity binding sites (2 S receptor) appear to be present in retina and pigment epithelium. A 5 S binding species is also present in pigment epithelium; it is similar in character to [3H]retinol binding in serum and may arise from serum contamination of the pigment epithelial preparation. Binding affinity in retina is high with possibly two classes of retinol binding sites present of KD about 1 - 10(-9) and 4 - 10(-8).

Animals↗
PubMed1977

Retinol receptors in corneal epithelium, stroma and endothelium.

Specific receptors for retinol are present in the cytosol fraction of corneal epithelium as demonstrated by sucrose density gradient centrifugation. These appear to be (1) protein in nature (2) of small molecular size (2 S) (3) specific for retinol and (4) present in several species. Assuming a receptor molecular weight of 15 000 and a single mole of retinol bound/mole of receptor protein, the association constant value is 5.26-10(7) with deltaG degrees = -8.53 kcal/mol. 2-S receptors are also observed in stroma and endothelium along with another binding species of approximately 8 S. Binding of [3H]retinol in bovine epithelial cytosol can also be demonstrated by disc gel electrophoresis and gel filtration. Immunodiffusion techniques demonstrate that monkey corneal epithelial and stromal cytosol samples do not contain contaminating serum retinol binding-protein.

Animals↗